1. Field of the Invention
The present invention relates to a repeater and a communication method for a packet communication network, and more particularly to a repeater and a communication method for sending and receiving a routing message according to a routing protocol.
2. Description of the Related Art
Routers for routing and forwarding packets in a packet communication network exchange packet relaying information called routing information between themselves and adjacent routers for accurately transmitting packets to dynamically changing packet destinations. The exchanged routing information keeps up to date routing tables which contain information representing an association between the addresses of destinations for packets to be relayed by routers and adjacent routers for relaying packets.
A protocol for exchanging routing information between adjacent routers is referred to as a routing protocol. According to the routing protocol, adjacent routers exchange not only routing information but also packets for confirming a connection between them thereby to detect a fault of such adjacent routers.
When a router detects a fault of an adjacent router in a packet communication network, the router which has detected the fault exchanges routing information for bypassing the faulty router between itself and an adjacent router other than the faulty router. The routers which have exchanged the routing information further exchange routing information with other routers adjacent thereto. In this manner, triggered by the fault of one router, exchanged routing information spreads to routers in the packet communication network, and each of the routers updates its routing table based on the exchanged routing information.
A large-scale packet communication network including many interconnected routers requires large-sized routing tables which pose a very high load on the CPU of each router for performing a routing table updating process. A router has a function to reboot itself to initialize its internal information for continuing normal operation when the load on its CPU becomes very high. If the routing table updating process spreads throughout the entire packet communication network, then many routers are caused to reboot themselves, tending to give rise to a communication shutdown in the packet communication network. When the faulty router recovers, routing information is exchanged again between the adjacent routers, making the overall packet communication network unstable.
According to one solution to the above problems, a function to send and receive packets for confirming connections and a function to send, receive, and store routing information, which are normally performed by a repeating controller, are carried out by packet repeaters for forwarding packets to adjacent routers. Therefore, even in the event of a failure of the repeating controller, routing protocol packets can properly be sent to and received from adjacent routers. The above technology is disclosed in Patent document 1 shown below.
According to the above technology, even when the repeating controller of a router suffers a fault, since packets for confirming connections are sent and received, adjacent routers do not the fault, and routing information is prevented from being exchanged between the adjacent routers and other routers. As routing information is continuously sent from the adjacent routers to the faulty router, the faulty router does not need to exchange routing information with the adjacent routers upon recovery from the failure by using the routing information which the repeating controller has received from the adjacent routers and stored during the fault. Therefore, the routers are prevented from suffering a chain of self rebooting due to the routing table updating process spreading through the packet communication network.
Patent document 1: JP-A No. 2003-258877
As described above, the technology disclosed in Patent document 1 makes it possible to avoid a communication shutdown in the entire packet communication network owing to a router fault. However, if a fault occurs in a communication path between routers, rather than a router itself, then since the routers are unable to send and receiver packets for confirming connections, they detect the fault and exchange routing information with adjacent routers in order to bypass the faulty route. In this case, if the routers are not prevented from suffering a chain of self rebooting due to the routing table updating process spreading through the packet communication network, then it is not possible to avoid a communication shutdown in the entire packet communication network owing to a router fault.